[Halld-tagger] Fixed array counters - corrected

[Richard Jones]

Dan and all,

When you mount the fixed array counters, do you foresee them hanging down from above (like stactites), or sticking up from below (like stalagmites)?  It might be more convenient from the point of view of cabling to have them above.  It would also help prevent collisions with the microscope, whose fiber readout is under the focal plane.  We are working on a scheme for shaping the ends of the box to allow fixed array access to the focal plane immediately below and above the microscope coverage.

-Richard J.


On 9/11/2012 4:57 PM, Alexander Somov wrote:
> Dear Dan, all,
>
> I think that the hodoscope rate in the microscope
> region is reasonable. I would go with a 4 mm counter
> size. The groups of counters also look good for me.
>
> I would require counters to overlap slightly in the
> close-packed region to avoid any acceptance gaps.
>
> How should we proceed with the counter location with
> respect to the focal plane ? Once we decide on this,
> we can ask Tim to prepare technical drawing for the
> mounting structure. Tim said that they may need
> about 1-2 extra cm if we decide to place counters at the
> focal plane
>
> We also need a few counters to cover the acceptance
> gap between the microscope scint. and the side plate of
> the microscope box.
>
> Dan, are you going to make some drawings for light guides ?
> I would use (straight) fish-tail light guides for
> all counters. For small counters (cnt22 + with R<20mm)
> we can just use a cylinder as a light guide. It would make
> sense to couple the light guides with PMTs in the same
> way.
>
> I would make the light guide about 5-6 inches long.
> The fringe field for end-pont counters is below
> 70 - 80 Gauss for both Bx and By at Y = 20 cm
> (and drops rapidly with Y).
>
>
> Thanks,
>          Alex
>
>
>
> On Tue, 7 Aug 2012, Daniel Sober wrote:
>
>> The previous mail, and Point 3 of the file attached to it, did not say quite
>> what I meant to.  Please look at the new pdf file instead.
>>
>> Here's my current best set of counters, with an explanation of the criteria
>> used.  Please look especially at point 3.  The important feature is that the
>> high-Egamma part of the hodoscope be able to run at GlueX rates.  I have set
>> it up so that the counters closest to the Microscope are 4 mm wide, compared
>> to the 2 mm Microscope fibers.  Thus no counter in this region counts faster
>> than twice the incoherent contribution in a microscope column.  Since the
>> microscope rate will be limited by the coherent peak, where the total flux is
>> ~twice as large, the maximum hodoscope counter rates will be ~ same as
>> Microscope column rate. Is this reasonable?  If not, I can easily re-do the
>> calculation with a different rate limit.
>> Dan
>> -- 
>> /Daniel Sober
>> Professor
>> Physics Department
>> The Catholic University of America
>> Washington, DC 20064
>> Phone: (202) 319-5856, -5315
>> E-mail: sober at cua.edu/
>>


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